In pattern or character recognition devices one approach is to assume that the object to be recognized belongs to a finite collection of patterns and also to assume that the object may be addressed by recognition devices on the basis that at no time will a given size field of view contain more than one pattern or character. This approach has been most successfully used in recognizing textual information such as printed alpha-numeric data. The more regular the printed matter, that it, the more stylized or regimented the character, the more successful the recognition device becomes in correctly identifying the character.
The development of character recognition devices has been toward an ideal device which could recognize a character with a relatively wide variation from the stylized form. Such a device would be capable of recognizing unconstrained hand printing and perhaps even handwriting. An important advance toward the attainment of the ideal is the incorporation of feature extraction in the recognition process. In feature extraction, the character under test is subjected to a large number of feature measurements to find the properties of the character, and if a sufficient number of properties exist belonging to a specific character value, then a probabilistic determination can be made that the character under test is recognized as a particular type. For example, a three and five each have a lower left tip. This property is invariant over a large number of type fonts. Consequently, a recognition of such a feature would identify the character as suitable for identification as one of those numbers. Further feature measurements can narrow the possibilities until a definite recognition is made.
The process, however, is complicated by many factors including the fact that characters may be produced by devices using different type fonts. It is complicated by the fact that characters produced by devices using the same type font may differ because of different printing pressure, age of the ribbon, wear of the print element or dirt on the print element. There may be a great deal of noise accompanying the character in the form of dirt or extraneous lines, and unconstrained hand print introduces not only wide character variation but also ball point pens that skip and graphite and ink that smear. Consequently, the design of a complete set of features enabling correct recognition in a high percentage of cases is an ongoing task through the life of a particular recognition device. As experience is gained with a recognition system, feature measurements are changed and added or subtracted to improve the percentage of correct identifications. Therefore, the improvement of feature extraction is an area of high engineering change activity, and it is a general object of this invention to provide a system in which feature measurements may be easily modified during both the design phase and the field life of the recognition device.
To provide a feature recognition system and device with the requisite changeability it is clear that the customary hard-wired logic circuits are difficult to change and therefore prohibitively expensive when change is necessary. Since hard-wired logic has been the usual approach in the past, character recognition devices have fallen far short of the ideal. Software approaches to implementing recognition logic have been devised and theoretically could be utilized for feature measurements in recognizing unconstrained character sets; however, due to the large number of measurements which must be made, the speed of recognition has been unsatisfactory and the process too expensive in the use of computer time. Thus while software is appropriately changeable it is inappropriately expensive and too slow. Therefore, it is another general object of this invention to provide sophisticated recognition equipment which is high speed as well as changeable.
In the implementation of the system of this invention, it is also necessary to produce the recognition function at a sufficiently low cost to produce a viable product. To that end it is another general object of this invention to design a system capable of utilizing devices which employ large scale integrated circuitry (LSI) in the feature recognition system.